Please explain the process stepbystep I am not looking for j

Please explain the process step-by-step. I am not looking for just an answer, but I am looking for a detailed description of how the answer was derived so I can see where I am messing up on my math. Thank you so much. Here is the answer from the answer key:

Solution

(a1 + a2 + a3)X = a1x1+ a2x2 + a3x3...........
composite foemula
part area xi yi xiai yiai

circle   4 2 2 8 8

rectangle1 6 -1.5 1 -9 6

rectangle2 4 -3.5 2 -14 8

tringle 1 1.125 -1 2.5 -1.125 2.8125

tringle 2 1.125 -2 2.5 -2.25 2.8125

X=-1.255/24.81=-.050558 ,Y=44.745/24.81=1.8035

x coordinate of rightangle tringle is 2/3 a

ycoordinate of rightangle tringle h/3